"We want justice and an end to impunity by the Border Patrol," said Ramon Valenzuela, one of the leaders of Wednesday's demonstration, which effectively shut down the port in both directions between 1 a.m. and 10 a.m.

Demonstrators blocking the northbound traffic at times clashed with Mexican farm workers eager to enter U.S. territory, but no serious injuries were reported.

Farm labor contractors in Imperial Valley, an important source of winter vegetables, reported a shortage of manpower after the protesters managed to strangle the normally bustling crossing.

Wednesday's protests was the largest and most effective of a series of such maneuvers that began last weekend and have become a source of increasing concern in Calexico, a California border town of 20,000 residents whose economic lifeline runs north from the much larger Mexican sister city of Mexicali. Long-term interruption of the flow of commerce could be devastating for the economies of both cities.

Sparking the demonstration was the shooting 11 days ago by an unidentified Border Patrol agent of Eduardo Garcia Zamores, a 15-year-old Mexicali youth who Mexican authorities say was shot as he was perched atop the 10-foot high metal fence delineating the international boundary line.

The youth, who was shot once, was in stable condition Wednesday at a Mexicali hospital with multiple internal wounds, authorities said.

It was the latest of a number of Border Patrol shootings that have provoked outrage among immigrant-rights advocates on both sides of the border.

A San Diego attorney representing the wounded boy said he planned to file a $9-million negligence claim today against the Border Patrol, contending that the youth was shot wrongly as he attempted to return to Mexico after having crossed, for perhaps 20 yards, into U.S. territory.

The attorney, Marco E. Lopez, who has handled a number of high-profile cases involving shootings by U.S. Border Patrol agents, says he also plans to request that Mexican authorities file a formal petition seeking the extradition of the agent to Mexico on criminal charges.

"The boy was shot in a position where he was not a threat to the agent," Lopez said.

The Border Patrol has yet to explain why the agent resorted to deadly force. Patrol policy, like that of other law enforcement agencies, requires that agents only fire their weapons to save their own lives or those of other innocent people.

Despite Lopez's efforts, the prospects for an extradition request seem remote. Marco Antonio Tovar, the Mexican consul in Calexico, said that Mexican officials would wait for the completion of FBI and Calexico police inquiries into the shooting before taking the extraordinary step of seeking the agent's extradition.

Border Patrol supervisors have refused to identify the agent involved in the latest shooting, in accordance with patrol policy. He has reassigned to desk duties pending the outcome of the investigations, the Border Patrol said.

The Mexicali-based protesters say they plan to continue periodic border blockades until action is taken in the shooting inquiry, a prospect that worries officials in Calexico.

The Mexicali-Calexico border is the second-busiest international crossing along the California-Mexico border after the San Ysidro facility in San Diego. Each month, about 2.6 million people and almost 700,000 vehicles enter Calexico from Mexicali.

Calexico's economy is driven by border trade, and the region's booming agricultural industry is largely dependent on the more than 1,000 Mexican farm workers who cross each day from Mexicali.

"Everyone wants the same thing: for justice to be done," said Calexico Mayor Ricardo Ortega, who made a trip to Mexicali on Wednesday to indicate his concern to his Mexican municipal counterparts. That followed a special session of the Calexico City Council on Tuesday night about the issue.

"We're a country of processes," said Mayor Ortega, who did not participate in the protests and did not comment on the Border Patrol shooting. "We just hope this process can be finished as quickly as possible."